Recent Developments in the Area of Thionation Methods and Related Synthetic Applications

Towards Symmetric Thioamides: Microwave-Aided Synthesis of Terephthalic Acid Derivatives

The multistep synthesis of novel bis-terephthalthioamides based on methyl esters of amino acids (AAs) was proposed using conventional heating and microwave-assisted approaches. In fact, the comparative case study on the thionation of new symmetrical diamides with Lawesson's reagent (LR) was performed. The microwave-accelerated small-scale methodology was successfully employed on the whole pathway from substrates (Gly, Ala, Val, Tyr, Ser) to products (symmetrical dithioamides of terephthalic acid), resulting in significantly reduced reaction time, energy requirements, and slightly increased reaction yields when compared to conventional heating. Moreover, the intermolecular similarity of novel terephthalic acid derivatives was estimated in the multidimensional space (mDS) of the structure/property-related in silico descriptors using principal component analysis (PCA) and hierarchical clustering analysis (HCA). The distance-oriented structure/property distribution was also correlated with the experimental lipophilic data.

Ph3P-mediated decarboxylative ring-opening of maleic anhydride by thiolic compounds: formation of two carbon-sulfur bonds

In this study, a simple and efficient method for the formation of carbon-sulfur bonds is described. In this process, ring opening of maleic anhydride by thiols or disulfides and triphenylphosphine led to the formation of sulfide products via formation of two carbon-sulfur bonds.

A Focused Review of Synthetic Applications of Lawesson's Reagent in Organic Synthesis

Lawesson's reagent (LR) is a well-known classic example of a compound with unique construction and unusual chemical behavior, with a wide range of applications in synthetic organic chemistry. Its main functions were rounded for the thionation of various carbonyl groups in the early days, with exemplary results. However, the role of Lawesson's reagent in synthesis has changed drastically, and now its use can help the chemistry community to understand innovative ideas. These include constructing biologically valuable heterocycles, coupling reactions, and the thionation of natural compounds. The ease of availability and the convenient usage of LR as a thionating agent made us compile a review on the new diverse applications on some common functional groups, such as ketones, esters, amides, alcohols, and carboxylic acids, with biological applications. Since the applications of LR are now diverse, we have also included some new classes of heterocycles such as thiazepines, phosphine sulfides, thiophenes, and organothiophosphorus compounds. Thionation of some biologically essential steroids and terpenoids has also been compiled. This review discusses the recent insights into and synthetic applications of this famous reagent from 2009 to January 2021.

Thionation of carbonyl compounds using phosphorus pentasulfide and hexamethyldisiloxane under microwave irradiations

A novel and convenient microwave assisted thionation of carbonyl compounds using phosphorus pentasulfide and hexamethyldisiloxane is described. Thionation by this method gave the desired product in higher yield and shorter reaction time as compared to conventional methods.

Self-assembled transition metal dithiocarbamates of pyridine-3-carboxamide: synthesis, spectral characterization, thermal and biological studies

Synthesis of self assembled transition metal dithiocarbamates of pyridine-3-carboxamide by conventional as well as in situ methodology was reported. Characterization was done with a variety of spectroscopic techniques. Anticancer and antioxidant activity of ligand and its complexes is also tested.

Decomposition of benzoylthioureas into benzamides and thiobenzamides under solvent-free conditions using iodine–alumina as the catalyst and its mechanistic study by density functional theory

Iodine–alumina catalyzed formation of benzamides and thiobenzamides through different paths by the microwave irradiation of benzoylthioureas.

Structural modifications of coumarin derivatives: Determination of antioxidant and lipoxygenase (LOX) inhibitory activity

In the present project, a series of coumarin analogues, were synthesised and evaluated for their antioxidant and soybean lipoxygenase inhibitory activity. A variety of structural modifications on the coumarin scaffold revealed interesting structure–activity relationships concerning the different biological assays. Prenyloxy-coumarins 9 and 10 displayed the best combined inhibition of lipid peroxidation and soybean lipoxygenase. Thiocoumarins 11 and 14 were identified as potent lipoxygenase inhibitors whereas hydrazone analogues 15 and 16 were efficient DPPH radical scavengers.

Thionations using a P4S10-pyridine complex in solvents such as acetonitrile and dimethyl sulfone

Tetraphosphorus decasulfide (P(4)S(10)) in pyridine has been used as a thionating agent for a long period of time. The moisture-sensitive reagent has now been isolated in crystalline form, and the detailed structure has been determined by X-ray crystallography. The thionating power of this storable reagent has been studied and transferred to solvents such as acetonitrile in which it has proven to be synthetically useful and exceptionally selective. Its properties have been compared with the so-called Lawesson reagent (LR). Particularly interesting are the results from thionations at relatively high temperatures (∼165 °C) in dimethyl sulfone as solvent. Under these conditions, for instance, acridone and 3-acetylindole could quickly be transformed to the corresponding thionated derivatives. Glycylglycine similarly gave piperazinedithione. At these temperatures, LR is inefficient due to rapid decomposition. The thionated products are generally cleaner and more easy to obtain because in the crystalline reagent, impurities which invariably are present in the conventional reagents, P(4)S(10) in pyridine or LR, have been removed.

Thionation of some alpha,beta-unsaturated steroidal ketones

The reactions of selected α,β-unsaturated steroidal ketones with Lawesson’s reagent (LR) in CH₂Cl₂ and toluene under the standard reaction conditions and with a combination of phosphorus pentasulfide with hexamethyldisiloxane (P₄S₁₀/HMDO) in 1,2-dichlorobenzene (ODCB) under microwave irradiation were investigated and for this purpose several cholestane, androstane and pregnane carbonyl derivatives were chosen. Depending on the reagent and the solvent, 19 new sulfur containing compounds, including dithiones 4c and 4d, α,β-unsaturated 3-thiones 3a-e, dimer-sulfides 2a-e, 1,2,4-trithiolanes 5a-e and phosphonotrithioates 6b-e were synthesized. All newly prepared compounds were characterized by IR, ¹H- and ¹³C-NMR spectroscopy and elemental analysis.

Mild method for the conversion of amides to thioamides

Aqueous ammonium sulfide was found to be an ideal substitute for hydrogen sulfide for the thiolysis of activated amides. High yields of the corresponding thioamides were obtained for a broad range of substrates, using two different procedures that are both operationally simple and inexpensive, as well as amenable to large-scale preparation. Preliminary results indicate that aqueous ammonium sulfide may also replace hydrogen sulfide in the synthesis of thionoesters from amides.